The present invention relates to a decker apparatus and to a method for separating a filtrate from a mass whose consistency is to be increased.
The above-mentioned apparatus and method are well known especially in pulp and paper industry and used for thickening, that is for increasing the consistency of various liquid-solid-compositions, for example, for the recovery of fibres from the effluents of a paper factory. Such an apparatus is disclosed, for example, in Finnish Patent No. 72051. The filtering process is based on the buildup of a filtering layer constituted of solid particles, which become deposited on the inner surface of the thickening drum. The filtrate leaving the mass flows through this layer as the drum rotates, and the thickness of the layer increases in the direction of rotation off the drum. The filtering layer is removed from the inner surface of the drum continuously with the help of spraying means located above the drum, and after this point, as the drum rotates further, new continuously growing filtering layer will begin to build up. The mass to be thickened is fed to the inside of the drum in axial direction at the end of the drum and the thickened mass is discharged through overflow at the opposite end.
Further, a decker under name AGP Vargo Filter is known on the market. In this apparatus, however, the surface of the liquid filtered out of the drum into the vat is on a relatively high level, surrounding the filter shell of the drum from outside, which reduces the pressure that can be utilized in filtering. Further, the initial filtrate of higher solid content filtered through the drum shell at the beginning of the filtration cycle can easily mix with the rest of the filtrate, because it can flow into the filtrate of higher purity, the flow taking place between the filter shell and a split baffle, which is intended for separation of the initial filtrate.